1. Field of the Invention
The present invention relates to a DC motor.
2. Description of Related Art
There is known a 6-pole DC motor for a starter, in which the field pole is comprised of permanent magnets. Generally, such a motor employs a wave-winding structure for an armature coil, and a 4-brush structure including two positive brushes and two negative brushes. As shown, for example, in Japanese Patent Application Laid-open No. 2003-189551, in such a motor, a lead wire connected to the positive brushes and drawn to the outside of the motor case thereof is disposed at substantially a middle position of the two positive brushes.
Meanwhile, some starters used for a vehicle have an idling stop function and accordingly are required to have a long life employ a 6-brush structure including three positive brushes and three negative brushes. Generally, in such a 6-brush structure, the lead cable is disposed between one of the positive brushes and one of the negative brushes which are adjacent to each other. The lead wire drawing position (the positon position at which the lead wire is disposed) of the DC motor employing the 6-brush structure is different from that in the DC motor employing the 4-brush structure. Accordingly, the same motor case cannot be shared between the 4-brush structure and the 6-brush structure.
In addition, to adjust the lead wire drawing position of the 6-brush structure to be the same as the lead wire drawing position of the 4-brush structure, since the lead wire drawing position circumferentially overlaps with the position of one of the negative brushes and accordingly a space for disposing therein the lead wire on the core side in the axial direction of the negative brushes is required, the overall motor length has to be increased.